Some radio communication apparatuses use quadrature modulation such as QAM (Quadrature Amplitude Modulation).
Many modulation schemes that use digital circuit technology use analog circuits for quadrature modulation. Since baseband analog signals are input into the quadrature modulator, the input signals inevitably include offsets such as amplitude offsets and direct current (DC) offsets.
When a signal input into I/Q inputs of a quadrature modulator in a radio communication apparatus that uses quadrature modulation includes a DC offset, the quadrature modulator outputs the DC offset as a carrier component. The carrier component remains as carrier leak and has adverse effects on communication performance such as reduction of reception sensitivity. In the worst case, carrier leak can cause a modulated wave to fail to meet specifications.
To prevent this, a technique for correcting a DC offset in a radio communication apparatus to reduce carrier leak (see JP 2007-208380A) has been proposed. JP2007-208380A discloses a radio communication apparatus in which a wave modulated by a quadrature modulator at a transmitting side is fed back to a receiving side in the radio communication apparatus, a DC offset value is calculated from the modulated wave at the receiving side, and a signal to be input into the quadrature modulator at the transmitting side is corrected on the basis of the calculated DC offset value.